Fix k8s client for handling empty list in response.

Implements: blueprint selflink
Change-Id: I0db851889017cfe19cc84acab36bdc67b04a9145

kuryr_kubernetes/k8s_client.py

@@ -133,12 +133,20 @@ class K8sClient(object):
             # for custom resources there are both kind and apiVersion..
             if kind.endswith('List'):
                 kind = kind[:-4]
+
+                # NOTE(gryf): In case we get null/None for items from the API,
+                # we need to convert it to the empty list, otherwise it might
+                # be propagated to the consumers of this method and sent back
+                # to the Kubernetes as is, and fail as a result.
+                if result['items'] is None:
+                    result['items'] = []
+
                 for item in result['items']:
                     if not item.get('kind'):
                         item['kind'] = kind
                     if not item.get('apiVersion'):
                         item['apiVersion'] = api_version
-            else:
+
                 if not result.get('apiVersion'):
                     result['apiVersion'] = api_version
         else:

kuryr_kubernetes/tests/unit/test_k8s_client.py

@@ -155,6 +155,27 @@ class TestK8sClient(test_base.TestCase):
 
         self.assertRaises(exc.K8sClientException, self.client.get, path)
 
+    @mock.patch('requests.sessions.Session.get')
+    def test_get_null_on_items_list(self, m_get):
+        path = '/test'
+
+        req = {'kind': 'PodList',
+               'apiVersion': 'v1',
+               'metadata': {},
+               'items': None}
+
+        ret = {'kind': 'PodList',
+               'apiVersion': 'v1',
+               'metadata': {},
+               'items': []}
+
+        m_resp = mock.MagicMock()
+        m_resp.ok = True
+        m_resp.json.return_value = req
+        m_get.return_value = m_resp
+
+        self.assertEqual(self.client.get(path), ret)
+
     @mock.patch('itertools.count')
     @mock.patch('requests.sessions.Session.patch')
     def test_annotate(self, m_patch, m_count):

kuryr_kubernetes/watcher.py

@@ -143,6 +143,12 @@ class Watcher(health.HealthHandler):
             LOG.exception(f'Error getting path when reconciling.')
             return
 
+        # NOTE(gryf): For some resources (like pods) we could observe that
+        # 'items' is set to None. I'm not sure if that's a K8s issue, since
+        # accroding to the documentation is should be list.
+        if not resources:
+            return
+
         for resource in resources:
             event = {
                 'type': 'MODIFIED',